A flush toilet system operates by the rapid passage of water from the cistern to the toilet bowl and then into to the underground sewer pipes. Water is stored in the cistern. Water is released from the cistern with the actuating of the flushing mechanism. Water passes through a cistern outlet into the bowl. When the water has drained from the cistern, the outlet valve reseals about the outlet and water from the mains water supply refills the cistern.
The outlet valve is usually a rubber or plastic gasket. Wearing of the cistern outlet valve prevents effective sealing of the outlet. Dirt in the water or scale deposits from chemically hard water can also obstruct the proper sealing of the cistern outlet valve. Often the amount of water that leaks through the cistern outlet valve as a result of ineffective sealing is very small and the leakage problem goes unnoticed. Even if a small trickle is noticed running down the inside of the toilet bowl, a person often does not bother replacing the seal because the trickle appears minimal. As the leakage problem causes no inconveniences to a person and the replacement of the cistern outlet valve itself is troublesome, there is little incentive to fix the leakage problem. Over a prolonged period, however, a significant volume of water escapes into the toilet bowl and is lost into the sewerage system. The loss of water from the cistern through an ineffective cistern outlet valve can be financially and economically significant particularly in times of drought.